The Developmental Origins of Behavioral Individuality

Every individual animal behaves differently, even if they have the same genome and have been raised in the same environment. This diversity in behavior challenges the notion that biological variation derives solely from differences in genetics and environment, and poses the question of what biological processes generate individuality. At very small scales, the dynamics of biological matter are essentially impossible to predict with certainty, and these stochastic fluctuations can ripple out to alter the metabolism, physiology, and behavior of cells and organisms. I review major findings related to the developmental origins of stochastic individuality. These include the multivariate, dynamic organization of individual behavioral differences; control of the extent of individuality by genes, neural activity, and neuromodulation; nanoscale features of neural circuits that predict behavioral biases at the individual level; and experimental and theoretical evidence that behavioral variability may reflect an adaptive bet-hedging strategy. I conclude with a brief discussion of how large datasets like connectomes and long-term behavioral recordings will inform our understanding of the mechanisms underpinning behavioral individuality.